The aorta is an elastic artery and as such is quite distensible, stretching and expanding when blood is forced into it from the left ventricle. This stretching creates the potential energy that helps maintain blood pressure during diastole; when the heart relaxes after contraction, the aorta contracts passively.
Myocardial perfusion is almost solely diastolic; the force that allows blood flow through the coronary arteries is dependent on the difference between the intra-aortic diastolic pressure and the left ventricular diastolic pressure. The coronary arteries originate from the aortic stem and penetrate the wall of the heart. Increased resistance to flow in the coronary arteries may be caused by atherosclerosis or increased diastolic intraventricular pressure from ischemia or cardiomyopathy, compromising coronary flow and causing myocardial ischemia.
Several clinical conditions are of relevance to the functioning of the aorta and control of blood flow during systole and diastole. Acute myocardial ischemia and other conditions cause cardiogenic shock, in which heart malfunction results in cardiac output inadequate for maintaining vital organ function. Pulmonary edema is a complication of cardiogenic shock that further impairs tissue oxygenation and may lead to death. Heart failure is also a chronic condition associated with increased morbidity and mortality and poor quality of life. In aortic regurgitation, impaired closure of the aortic valve causes retrograde blood flow from the aorta into the left ventricle during diastole, resulting in increased diastolic intra-aortic pressure, ventricular volume overload and left ventricle (LV) dilatation and eventually congestive heart failure.
Currently medical management of ischemic heart disease is primarily focused on slowing atherosclerosis, preventing thrombosis and coronary angioplasty using catheterization and coronary bypass surgery. Chronic heart failure is usually treated medically but may require heart transplantation or use of a Left or Right Ventricular Assist Device (L- or R-VAD).
Heart transplantation is problematic in that there are insufficient donors and immunosuppression is required. While LVAD can be used in the long-term it is generally used for those awaiting donor hearts and is patients are plagued by infection and require anticoagulants to prevent blood clotting caused by the blood passing over non-biological surfaces. Intra-aortic balloon pumps may be inserted in the case of acute LV failure unresponsive to treatment but this treatment is limited to a short period of time due to infection and thrombotic complication. Aortic regurgitation is treated medically by drugs that reduce the arterial resistance (after-load reduction) or by aortic valve replacement in advanced disease. Reducing LV diastolic pressure by pre- and after-load reduction by nitrates and diuretics is the mainstay of treatment in case of pulmonary edema.
Heart contractions are controlled by electrical impulses created by cardiac pacemaker cells but for many years artificial devices have been installed after damage to the body's intrinsic conduction system to produce these impulses synthetically. These existing artificial pacemakers are medical devices designed to regulate the beating of the heart itself. More recently implantable cardioverter-defibrillators (ICD) resembling cardiac pacemakers have been used in patients at risk of sudden cardiac death. ICD's have the ability to treat many types of heart rhythm disturbances by means of pacing, cardoversion or defibrillation. The device contains the rudiments of cardiac arrhythmia detection and treatment and primarily deals with ventricular fibrillation but is now also used to deal with atrial and ventricular arrhythmias. ICD implantation is similar to implantation of a cardiac pacemaker, these devices typically include a wire that runs through the right chambers of the heart and usually ends in the apex of the right ventricle. They constantly monitor the rate and rhythm of the heart and can deliver therapies when the heart rate goes over a certain number: sensors can detect rate discrimination, rhythm discrimination and morphology discrimination.
In the aortic pacemaker constant monitoring of a wide variety of parameters means that it may be activated chronically for congestive heart failure, aortic regurgitation or aortic aneurysm, or activated in a chronic-intermittent manner, for example in the case of exertional angina. The pacemaker can be used for acute incidents such as cardiogenic shock or for a limited period of time following myocardial infarction or myocarditis.
As can be seen medical and surgical treatment for heart conditions are limited and many of the surgical procedures are highly invasive and prone to infection or involve high risk surgery. While pacemakers of various types exist, these are used to regulate cardiac conduction. There is an obvious clinical benefit to globally increasing coronary blood flow, but no such treatment is available. In addition there is no treatment apart from aortic valve replacement to selectively and efficiently block blood regurgitation to the LV in aortic valve insufficiency. Thus an aortic pacemaker to selectively pace the aortic media is a long-felt need.